import torch.nn as nn

from engine.BiRefNet.models.modules.utils import build_act_layer, build_norm_layer


class StemLayer(nn.Module):
    r"""Stem layer of InternImage
    Args:
        in_channels (int): number of input channels
        out_channels (int): number of output channels
        act_layer (str): activation layer
        norm_layer (str): normalization layer
    """

    def __init__(
        self,
        in_channels=3 + 1,
        inter_channels=48,
        out_channels=96,
        act_layer="GELU",
        norm_layer="BN",
    ):
        super().__init__()
        self.conv1 = nn.Conv2d(
            in_channels, inter_channels, kernel_size=3, stride=1, padding=1
        )
        self.norm1 = build_norm_layer(
            inter_channels, norm_layer, "channels_first", "channels_first"
        )
        self.act = build_act_layer(act_layer)
        self.conv2 = nn.Conv2d(
            inter_channels, out_channels, kernel_size=3, stride=1, padding=1
        )
        self.norm2 = build_norm_layer(
            out_channels, norm_layer, "channels_first", "channels_first"
        )

    def forward(self, x):
        x = self.conv1(x)
        x = self.norm1(x)
        x = self.act(x)
        x = self.conv2(x)
        x = self.norm2(x)
        return x
